Personally, im no expert, I would rather setup down the long axis of the room.
Do the doorways have doors? is yes, then they arent a big deal if they are open it will affect things.
For acoustic panels GIK seem to be very popular for panels, there are plenty of other brands but I see the most GIK panels on store walls and in setups here.
System: Cambridge 851A, Revel M126be, SVS SB2000, Cambridge DACMAGIC 100, JVC XL-Z1050TN, Rega RP6, Vincent PHO-8. A bunch of monster power conditioning junk V: Samsung NU8000, Nvidia Shield TV